1. Field of the Invention
The Invention relates to a device and a method for the manufacture of cement clinker, also referred to as clinker. The device has a kiln to bake raw meal into clinker. Flue gas escapes from an exhaust of the kiln.
2. Description of Relevant Art
Clinker is manufactured by baking raw powder meal in a kiln. This requires a temperature of about 1450° C. To generate this temperature, energy carriers such as coal, natural gas, crude oil, crude oil products (e.g. plastic residue), paper, wood or other replacement fuels are burned in the kiln. This combustion leads to the generation of flue gases that contain nitrous oxides (NOx) and therefore have to be subjected to denitrification. This means conversion of nitrous oxides with a reduction agent such as ammonia (NH3), in the presence of oxygen to form water (H2O) and nitrogen (N2). The reaction temperature required for the conversion of nitrous oxides can be reduced by using catalyzers, e.g. of titanium dioxide (TiO2), tungsten trioxide (WO3) or vanadium pentoxide (V2O5). Such catalytic denitrification is also referred to as SCR, meaning “Selective Catalytic Reduction”. Accordingly, the abbreviation SNCR (“Selective Non Catalytic Reduction”) means non-catalytic denitrification. SCR for denitrification of flue gases of rotary kilns for clinker manufacture is described, for example, in patent application DE 197 56 392 A.
The flue gases of the kiln are dust-loaded and escape from the kiln at a temperature in the range of 900-1100° C. These flue gases are used to preheat the raw meal in raw meal preheaters and to deacidify it. This is usually done using cascaded cyclone separators, usually placed in heat exchanger towers. The flue gases escaping from the raw meal pre-heaters would have a temperature sufficient for SCR-denitrification, but are still charged with fine dust that has an abrasive effect on the catalyzer and may cause clogging of the catalyzer. Therefore, it is suitable for dedusting the flue gases before SCR-denitrification. There are filters with which approx. 450° C. hot gases can be dedusted, which are referred to as hot-gas filters. However, they are expensive and large. Use of bag filters is easier, but they require much lower flue gas temperatures, so that the flue gases must be cooled, filtered and then reheated to the temperature required for the catalytic reduction. This setup is also referred to as “Low Dust” or “Tail End” configuration.
DE 10 2010 004 011 B3 discloses a method and a system for manufacture of cement clinker. As usual, clinker is sintered in a rotary kiln that emits exhaust gas as well referred to as flue gas. The exhaust gas is supplied to a raw meal preheater, escapes from it and is denitrified in a downstream SCR-catalyzer. The exhaust gas is first cooled in a cooling tower, then dedusted in a filter and finally heated to the temperature best for the SCR catalyzer in a heat exchanger. As a heat source, the flue gas heated by SCR denitrification is supplied to the heat exchanger on its hot side. The heat exchanger, therefore, is a recuperator.
EP 0 461 305 81 discloses a procedure to clean the exhaust gas of a cement clinker line. The flue gas escaping from a kiln of which is guided to a heat exchanger tower for raw meal preheating. Then the flue gas either feeds a raw material mill or a cooling tower and is then recombined and supplied to a multi-level filter system. The first filter is an electrostatic dust filter. It is connected to a second filter stage with three filter chambers built as fixed-bed reactors. Before both filter stages, fresh air is added to the flue gas flow, which cools off the flue gases.